A driveline of a vehicle may include a torque converter that provides torque multiplication and driveline dampening. The torque multiplication can improve vehicle acceleration from zero speed, but the torque multiplication is a result of operating an engine or motor at a higher speed to create slip across the torque converter. The engine, motor, and torque converter may operate less efficiently when there is a large amount of slip across the torque converter (e.g., a large speed differential between a torque converter impeller and torque converter turbine). Consequently, powertrain efficiency may be reduced more than is desired during vehicle launch. Nevertheless, it may be desirable for the torque converter to operate with a large amount of slip between the torque converter impeller and the torque converter turbine when a driver is requesting a large amount of torque so that the vehicle may accelerate more rapidly.
The inventors herein have recognized the above-mentioned issue and have developed a driveline operating method, comprising: accelerating a torque converter impeller to a desired speed in response to release of a brake pedal; and maintaining a torque converter impeller speed profile at the desired speed in the presence of an increase in driver demand torque until a torque converter turbine speed is within a threshold speed of the torque converter impeller speed.
By maintaining torque converter impeller speed at a constant or varying desired value, it may be possible to provide the technical result of improved torque converter and driveline efficiency. The constant torque converter impeller speed may allow torque converter turbine speed to approach torque converter impeller speed sooner so as to reduce torque converter slip. Additionally, in some cases where a driver requests greater amounts of torque, the device driving the torque converter impeller may transition between a speed control mode and a torque control mode to improve vehicle acceleration. In some examples, the control of torque flow through the torque converter may be based on a virtual torque converter impeller speed which may improve estimates of torque transferred through the torque converter.
The present description may provide several advantages. Specifically, the approach may provide more consistent vehicle launches under similar operating conditions. Further, the approach may improve driveline efficiency while at the same time providing the capacity to accelerate at a higher rate when requested by driver demand. Further still, the approach compensates for delays in torque converter clutch lockup operation so that a driver may experience a more acceptable rate of vehicle acceleration.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.